Many growth factors are known to play important roles in the early wound healing process. However, their roles in the subsequent scar formation phase are relatively unexplored. The aim of this study is to investigate how these factors affect DNA and collagen synthesis by scar fibroblasts in the scar formation process. Experimental wounds were made by excising palatal mucosa of eight-week-old SD rats. One month later, immature scar tissues were secured from the palate and scar fibroblasts (SF) were obtained from explant cultures of these tissues. Normal fibroblasts (NF), used for control, were obtained from palatal mucosa of untreated animals by the same culture procedure. SF had more slender shape than NF in stationary phase. SF showed longer doubling time, higher collagen synthesis and relatively higher type III collagen formation compared with NF. PDGF and EGF stimulated [3H] Thymidine uptake less effectively in SF than in NF. TGF-beta had no effects on [3H] Thymidine uptake when it was added alone. However, when TGF-beta was administrated in combination with EGF, the EGF-induced stimulation in DNA synthesis was suppressed dose-dependently. TGF-beta stimulated collagen synthesis more effectively in SF than in NF. These data may explain the reason for the accumulation of collagen and the increase in cell number during the scar formation process.